Extrude while sliding
To scale the outer loopcut (like Edge Slide with Clamping enabled does) scale along normals.
Press E to extrude and Esc to cancel. There were created double vertices which have the same position as their parent vertices.
Now press Alt+S to scale along normals.



Note that after the scale procedure is done scaling won't provide the same result as normals' orientation for newly extruded vertices changed; they will move towards the view point because of that (Edge Slide will work instead).